1. Field of the Invention
The present invention relates to a technique to cope with an abnormal increase of a secondary pressure in a pressure regulator for a fuel gas which is fed to a burner from a gas container with its pressure reduced to a predetermined pressure by the pressure regulator.
2. Prior Art
It is known in the art that a pressure regulator for a fuel gas has the construction that a primary passage and a secondary passage are connected to each other through a pressure reducing valve. When the pressure reducing valve goes wrong or a foreign substance is caught in the valve seat thereof, the pressure reduction function of the the valve is disordered and hence the pressure in the secondary passage is increased abnormally. thereupon, an abnormal combustion or a flame-out is caused in the burner with being attended with danger.
As a means to cope with the abnormal increase of the secondary pressure, such a regulator has so far been on the market, for example as the pressure regulator used for the LPG container which is placed outdoors and of which the secondary pressure is kept in the predetermined pressure by releasing a certain amount of fuel gas to the atmosphere through the relief valve connected to the secondary passage.
On the other hand, the inventor of the present invention invented such a regulator (hereinafter referred to as a previously conceived embodiment) as shown in FIG. 4, wherein a diaphragm cylinder 170 as an actuator is driven by the abnormally increased pressure in a secondary passage 150 and then a valve body 70 in a shutoff valve 50 is pushed to the shutoff position by the cylinder through an output rod 122 and a valve rod 70c, wherein the primary passage is closed.
However, the pressure regulators in the abovementioned prior art have following problems.
A. In the case of the former regulator brought to market: In spite of its advantageous feature that the abnormal increase of the secondary pressure therein attended with the danger can be prevented effectively, the regulator has the following problems.
(a) The regulator is in danger of deriving a secondary accident from the ignition of the fuel gas released to the atmosphere by the relief valve. Especially, in a gas oven equipped with a gas cartridge therein, as a fuel gas is to be released near the burner thereof, the danger of firing is brought more conspicuous.
(b) Even though an abnormal condition such as a fuel gas release from the actuated relief valve is caused, it might not be noticed by anybody because the burner can keep the normal combustion continuously. Therefore, in order to detect such a dangerous condition, it is necessary to provide for a gas-leak alarm.
(c) The gas fuel released to the atmosphere by the relief valve is wasted in the result.
B. In the case of the latter regulator as the previously conceived embodiment: The regulator has the advantagous feature that it can solve such foregoing problems of (a) through (c) as itemized above in the prior art embodiment, but it still has the following problems.
(d) Even though an O-ring 50c is provided for sealing the gap between the valve rod 70i c and the through-hole 50b, which is bored in the end wall 50a of the valve chamber 60 in the shutoff valve 50, a danger of a gas leak due to an injury of the O-ring 50c is still remained.
(e) The outward pushing force by the primary pressure and the frictional resistance force by the O-ring 50c exert on the valve rod 70c and, in the result, affect upon the diaphragm cylinder 170 as a large operational resistance force. That is, the primary pressure functioning as the outward pushing force to the valve rod 70c is about 100 times as high as the secondary pressure functioning as the driving force to the diaphragm cylinder 170 (for example, in the case of the gas oven equipped with the gas cartridge, the primary pressure of butane gas is ab.3 kg/cm.sup.2 and the secondary pressure thereof is 280 mm aq.). In addition thereto, the O-ring 50c has to exert the substantially high frictional resistance force onto the rod 70c in order to seal the high primary pressure. Therefore, it is necessary that the pressure receiving area of the diaphragm cylinder 170 has to be enlarged in order to operate accurately according to the low secondary pressure.
(f) ln case that the O-ring 50c is glued to the valve rod 70c by its secular degeneration, the diaphragm cylinder 170 becomes impossible to actuate the valve body 70 in the shutoff valve 50 through its output rod 122 and the valve rod 70c, and hence the reliability of the shutoff valve is lowered.